D.Gray-man follows the adventures of 15-year-old Allen Walker, whose left arm can transform into a monstrous claw and destroy akuma, evolving machines created by the Millennium Earl to help him destroy humanity. As ordered by his master General Cross Marian, Allen becomes an Exorcist, one of the warriors dedicated to the destruction of akuma and the protection of innocence.
He is sent to the Black Order, an organization comprised of Exorcists, which is led by the mysterious Millennium Earl. Joining Allen in his quest are his fellow Exorcists, each with their own unique abilities. Together they battle against the Earl and his demonic army to protect the world from destruction.